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Natasha Hetrick '05

Analysis of Vitamin K Levels in the Diets of Female Endurance Runners

Vitamin K has a critical role in bone metabolism indicated by recent research on women with osteoporosis. Postmenopausal women increased their bone density after supplementation with vitamin K suggesting that the current Adequate Intake level (AI) of 90 µg for women over age 19 may be inadequate for bone health.

Purpose: The purpose of this study was to examine the vitamin K intake of female endurance runners’ diets to assess if they are currently consuming the AI for vitamin K and to combine this information with their health history to determine if there is a connection between lower vitamin K intakes and stress fractures.

Methods: This study included 13 intercollegiate female endurance runners between ages 19-22. The currently available nutritional analysis software does not include sources of vitamin K; therefore, a Food Frequency Questionnaire specifically designed to identify vitamin K intake based on the USDA database was utilized. Participants completed this Food Frequency Questionnaire, and an additional survey to assess activity level, menarche status, pertinent medications, all dietary and herbal supplements, and stress fracture history, and they completed a 7-day diet and physical activity record.

Results: Mean vitamin K intake was 360.9 µg [range was 42.7- 610.0 µg]. However, 5 of the 13 participants’ weekly vitamin K intakes were below the current AI. Six participants reported stress fractures—only one of these had a mean vitamin K intake less than the AI. Six subjects were taking multi-vitamin supplements with calcium and vitamin D, and 6 subjects were using oral contraceptives.

Conclusions: Vitamin K did not correlate directly with stress fractures. The supplements with calcium and vitamin D, and the oral contraceptives may offer extra bone protection. All participants’ day-to-day intake varied greatly. Subjects with particularly high vitamin K intakes tended to consume more spinach, lettuce, tofu, green vegetables, olive, and/or canola oils than participants with lower vitamin K intakes.

Research Advisor: Amy Olson, PhD, RDN, LD